1. Field of the Invention
The present invention relates to an optical fiber connecting member for forming optical connecting by facing end portions of optical fibers each other, a method of producing the optical fiber connecting member, and a method of connecting optical fibers.
2. Description of the Related Art
Accompanying with the development of optical communication networks, optical fiber connecting has been required to satisfy low loss, low cost, high reliability and easiness of connecting. From this point of view, a fusion connecting method for fusing end portions of optical fibers with each other and a mechanical connecting method for retaining end portions of optical fibers merely in a physically facing state have been mainly developed as a stationary optical fiber connecting method for forming an optical communication network.
As the fusion connecting method, there is generally known a method in which heat-fusion is performed by means of arc discharge, or the like, after planishing connecting end surfaces of single-core or multi-core optical fibers, facing the connecting end portions of the optical fibers with each other through a V-groove and making axis alignment of the optical fibers by a moving mechanism under microscopic observation, for example, as described in Unexamined Japanese Patent Publication (kokai) No. Hei-2-281207.
As the mechanical connecting method, there is known a method in which optical fibers are fixed physically by an adhesive agent in the condition in which end portions of the optical fibers are inserted into a through-hole of a sleeve-like connecting member from opposite ends of the connecting member so as to be faced each other, for example, as described in Unexamined Japanese Patent Publication Nos. Sho-61-25109 and Hei-2-103004. With respect to multi-core optical fibers, there is also known a method in which optical fibers are fixed physically by heat-fusing a plurality of glass pipes or a body obtained by uniting the plurality of glass pipes after inserting the optical fibers into the pipes through V-grooves provided in opposite ends of the pipes, for example, as described in Unexamined Japanese Patent Publication No. Sho-59-228214. Besides the aforementioned methods, there is further known a method in which: optical fibers are faced each other in V grooves or inserted into a member having its inner diameter finished with high accuracy so as to be faced each other through V groves and pressure-stuck to each other by upper and lower plate members, or the like, to thereby fix connecting physically.
The fusion connecting method in which low-loss high-reliable connecting can be made, has however a problem in that a fusion-connecting apparatus for fusion connecting is expensive, in that a high-grade technique is required for retention of optical fibers, axis alignment of optical fibers, joining of optical fibers, or the like, by the fusion-connecting apparatus, and in that the time required for connecting becomes long.
On the other hand, the mechanical connecting method in which low-cost connecting can be performed by a simple technique of fixing optical fibers by inserting or arranging the optical fibers in a connecting member prepared in advance, has a problem in that this method is poor both in connecting loss and in reliability. The problem in the mechanical connecting method is mainly caused by discrepancy in axis of optical fibers forming connecting and by fixture of connecting. As a measure to solve the problem, the problem can be improved to some degree by highly accurately forming the optical fiber insertion through-hole of the connecting member.
Because optical fibers having an outer diameter of 125.mu.m are generally used, it is however difficult to accurately form the through-hole having a diameter slightly larger than the outer diameter of the optical fibers. Even if the through-hole can be formed accurately, it is difficult to insert optical fibers into the through-hole which is smaller than a needle hole. Therefore, the optical fiber inlet of the through-hole of the connecting member is required to be provided as a conical hole to facilitate insertion of optical fibers or a V-groove table is required for insertion guiding. With respect to connecting of single-core optical fibers, the problem upon insertion can be solved to some degree by providing these means.
In the case of connecting of multi-core fibers, especially in the case of connecting of tape-shaped multi-core optical fibers, however, a plurality of optical fibers should be inserted into a plurality of through-holes simultaneously because ends of the optical fibers are cut so as to be arranged in one line. Even if the ends of the optical fibers are cut so as to be arranged in one line accurately, the distances between the ends of the multi-core optical fibers may be widened by rebound due to electrification or the distances are not always uniform because the distances between optical fibers, especially tape-shaped multi-core optical fibers, may be designed intentionally so as to be different from each other in order to facilitate separation from each other. Accordingly, skill and labor is required because it is difficult to connect multi-core optical fibers even if the optical fiber inlets of the through-holes of the connecting member are provided as a conical hole or even if a V-groove table is provided for insertion guiding. Further, V-grooves should be made coincident with the inlets of the optical fiber connecting member because the optical fiber connecting member and the V-groove table are formed separately. Accordingly, considerable accuracy on production is required, so that increase in cost is brought about.
Further, in order to fix optical fibers in the connecting member, fusion fixture by means of fusion of the connecting member, fixture by means of an adhesive agent or mechanical fixture using upper and lower plates, or the like, is supposed. In the case of fusion fixture by means of fusion of the connecting member, discrepancy in the axis of optical fibers occurs easily because of heat and fluidity at the time of fusion of the connecting member. In the case of fixture using an adhesive agent, not only a large time is required for hardening the adhesive agent but also discrepancy in axis of optical fibers occurs easily at the time of the hardening of the adhesive agent. In the case of mechanical fixture using upper and lower plates, or the like, not only discrepancy in axis of optical fibers occurs in the same manner as described above but also mechanical distortion is given because pressure is applied to sides of optical fibers. In any fixture, there is a cause of the increase of the connecting loss.